Methods and devices for connecting nerves

ABSTRACT

A nerve repair conduit configured to be secured on first and second portions of a selected nerve. The nerve repair conduit includes a polymeric body having a proximal end, a distal end, an exterior surface and an interior surface defining an interior lumen. In addition, the nerve conduit includes at least one drug reservoir to hold agent(s) that may facilitate nerve regeneration. The drugs diffuse from the drug reservoir(s) into the nerve repair conduit through an outlet (such as a hole or a semipermeable membrane) in proximity to the first and second portions of a selected nerve. The nerve repair conduit may be configured to deliver the agent(s) at a rate having substantially zero-order kinetics and/or at a constant rate over a selected period of time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 15/942,965 filed 2 Apr. 2018 and titled “METHODS AND DEVICES FOR CONNECTING NERVES,” which is a continuation of U.S. patent application Ser. No. 14/352,024 filed 15 Apr. 2014 and titled “METHODS AND DEVICES FOR CONNECTING NERVES,” which application claims the benefit of and priority to International Application No. PCT/US12/60439, filed 16 Oct. 2012 and titled “METHODS AND DEVICES FOR CONNECTING NERVES,” which claims the benefit of and priority to U.S. Prov. Pat. App. Ser. No. 61/689,263 filed 1 Jun. 2012 and titled “METHODS AND DEVICES FOR CONNECTING NERVES”, U.S. Prov. Pat. App. Ser. No. 61/634,362 filed 28 Feb. 2012 and titled “METHODS AND DEVICES FOR CONNECTING NERVES,” and U.S. Prov. Pat. App. Ser. No. 61/547,978 filed 17 Oct. 2011 and titled “METHODS AND DEVICES FOR CONNECTING NERVES,” the entireties of each of which are incorporated herein by this reference.

BACKGROUND

Peripheral nerve injuries affect 2-3% of trauma patients and vastly more subsequent to tumor extirpation or iatrogenic injury. These injuries can result in chronic debilitating pain from crush or neuroma formation. Patients often suffer from life-long loss or functional disturbances mediated by the injured nerve, which can severely diminish their quality of life. Nerve injuries have a tremendous socioeconomic impact from loss of work and associated healthcare costs. Nerve lesions caused by trauma, tumor or inflammatory processes often require the removal of the injured segment of nerve and subsequent repair either by tension free end-to-end neurorrhaphy or by bridging the gap with autologous nerve grafts or nerve conduits. Inadequate or untimely repair can result in lifelong deficits in muscle function or sensation.

The current standards for repairing gaps that cannot be brought together without tension require bone shortening to allow for a tension-free repair, or the use of an autologous nerve graft. These grafts are harvested from donor sensory nerves (sural nerve or posterior interosseous nerve) and have the disadvantage of loss of sensation at the donor site as well as the need for an additional surgical site. While autologous nerve grafts serve as the state-of-the-art in repairing nerve gaps, numerous challenges associated with this approach results in functional benefits to less than about 50% of patients (e.g., only about 40-50%). These challenges include morbidity at the site of harvesting of donor nerve(s), limitations to the amount of nerve that can be harvested, mismatches in size and fascicular patterns between the nerve stumps and the graft. In recent years, grafts made from biologically derived materials have gained traction over allogenic and xenogenic tissues. Collagen, fibrin, and fibronectin have been used in addition to synthetic materials such as aliphatic polyesters and hydrogels. Much progress has been made in the field of artificial nerve conduits with collagen and polyglycolic acid conduits commercially available and in use. These hollow tubes act as axon guides for the regenerating nerves and can allow for tension free bridging without the need to harvest donor nerve.

Separately, it has been shown that locally delivering growth factors or small molecules can enhance axon sprouting and peripheral nerve recovery. In animal models, a variety of proteins or small molecules including Galectin-1, VEGF, Nerve Growth Factor (“NGF”), FK506, GDNF, and Netrin-1, for example, delivered locally can act to direct axon growth, enhance Schwann cell migration and/or enhance axon regeneration. Acellular conduits and scaffolds have limited regenerative capacity and depend on the migration of supporting cells into the local environment. Local delivery of growth factors have shown promise in recruiting nerve growth promoting cells like Schwann cells and endothelial cells and in promoting direct axon growth.

BRIEF SUMMARY

The present disclosure relates to nerve repair conduits, kits that include such conduits, and methods for using such conduits. The nerve repair conduits described herein are configured for covering a damaged portion of a nerve and deliver one or more drugs thereto increase the rate of functional recovery. For example, with a transected nerve, the nerve repair conduits described herein may secure a proximal portion of the severed nerve in proximity to a distal portion of the severed nerve. The conduits described herein may, for example, be positioned around injured (e.g., crushed), partially transected, or fully transected nerves end-to-end, end-to-side, side-to-end or side-to-side. In addition, the nerve repair conduits described herein include drug reservoirs that are positioned on the conduits inside the body (i.e., in vivo) at the site of nerve repair without the use of an external drug conduit, thus (1) continuously delivering small molecules or growth factors to the adjoined nerves at a controlled rate and (2) improving the degree of axon regeneration and functional recovery. These nerve conduits are unique in that the desired drug(s) or other agents are released from an integrated (i.e., in situ) reservoir through an outlet (e.g., a semi-permeable membrane) into the conduit lumen in proximity to the injured nerve. This delivery configuration can allow for more controlled and uniform delivery of one or more compounds rather than relying on drugs embedded in biodegradable conduits or drugs that are administered from outside the body, which may have inconsistent delivery kinetics and significant burst effects.

In one embodiment, a nerve repair conduit includes a polymeric body having a proximal end, a distal end, an exterior surface and an interior surface defining an interior lumen. The nerve repair conduit further includes one or more drug reservoirs associated with the outer surface of the polymeric body. The drug reservoirs are configured to hold a liquid or diffusible agent. Suitable examples of agents include small molecule drugs, proteins (e.g., NGF), DNA or RNA, viruses, and the like. The agent may be in liquid form, or in a suspension, a gel, a hydrogel, in a polymer matrix, or the like. In addition, the one or more drug reservoirs may be loaded with cells (e.g., Schwann cells or adipose-derived stem cells) or other bioactive agents that may aid nerve repair and recovery. In one embodiment, the one or more drug reservoirs may contain an excipient and at least one agent. The nerve repair conduit further includes one or more outlets (e.g., one or more semipermeable membranes and/or diffusion holes) formed between the one or more drug reservoirs, the exterior surface of the polymeric body, and the interior surface of the polymeric body for delivering the at least one drug to the interior lumen of the polymeric body.

In one embodiment, the nerve repair conduit is configured to deliver at least one drug at a rate having substantially controlled kinetics (e.g., substantially zero-order or substantially first-order kinetics) over an extended period of time—e.g., at least one week, two weeks, three weeks, at least one month, or longer. In another embodiment, the nerve repair conduit may be configured to deliver at least one drug at a substantially constant rate (e.g., a selected amount of drug is delivered from the reservoir to the interior lumen per unit time) over an extended period of time—e.g., at least 24 hours, one week, two weeks, three weeks, at least one month, or longer.

In another embodiment, a method for repairing a nerve is disclosed. The method includes (1) providing a nerve repair conduit as described above, (2) securing the proximal end of the nerve repair conduit on a first portion of a nerve and securing the distal end of the nerve repair conduit on a second portion of a nerve such that the first and second portions are in fluid communication with one another via the interior lumen of the nerve repair conduit, and (3) infusing the first and second portions with at least one agent from the one or more drug reservoirs that are associated with the conduit. The first and second portions may, for example, include proximal and distal portions of an injured but still intact nerve (e.g., a crushed nerved), or the first and second portions may include proximal and distal portions of a partially or fully transected nerve. In one embodiment, the at least one agent may be delivered at a rate having substantially controlled kinetics (e.g., substantially zero-order or substantially first-order kinetics and over an extended period of time—e.g., at least one week, two weeks, three weeks, at least one month, or longer. In another embodiment, the at least one agent may be delivered at a substantially constant rate over an extended period of time—e.g., at least 24 hours, one week, two weeks, three weeks, at least one month, or longer.

In a specific embodiment, the nerve repair method described herein may include positioning a nerve graft in the nerve repair conduit, and securing the proximal end of the nerve repair conduit on the selected portion of the first nerve and securing the distal end of the nerve repair conduit on the selected portion of the second nerve such that the nerve graft acts as a bridge between the first and second nerves.

These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is appreciated that these drawings depict only illustrated embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

FIG. 1A illustrates a nerve repair conduit, according to one embodiment of the present invention;

FIG. 1B illustrates a nerve repair conduit, according to one embodiment of the present invention;

FIG. 2A illustrates an end cut-away view of the nerve repair conduit illustrated in FIG. 1B, according to one embodiment of the present invention;

FIG. 2B illustrates a side cut-away view of the nerve repair conduit illustrated in FIG. 1B, according to one embodiment of the present invention;

FIG. 3A illustrates a side elevation view of a nerve repair conduit adjoining a transected nerve in an end-to-end fashion, according to one embodiment of the present invention;

FIG. 3B illustrates a partial cut-away view of a nerve repair conduit adjoining a transected nerve in an end-to-end fashion, according to one embodiment of the present invention;

FIG. 3C schematically illustrates a partial cut-away view of a nerve repair conduit adjoining a transected nerve in a side-to-side fashion, according to one embodiment of the present invention;

FIG. 4 illustrates a partial cut-away view of a nerve repair conduit that includes a nerve graft adjoining a transected nerve with the nerve graft positioned between the nerve ends, according to one embodiment of the present invention;

FIG. 5 is a graph illustrating the cumulative amount of bovine serum albumin (“BSA”) released in a simulated drug release/leakage test with a nerve repair conduit as described herein;

FIG. 6 is a graph illustrating the percentage of BSA released versus time in the simulated drug release/leakage test with a nerve repair conduit as described herein;

FIGS. 7A through 7C illustrate a partial cross-sectional view of a nerve repair conduit coupled to a transected nerve, showing the progressive growth of a proximal nerve end toward a distal nerve end as axons of the nerve regenerate over time;

FIG. 8 illustrates a partial cross-sectional view of another embodiment of a nerve repair conduit configured to provide a concentration gradient of one or more drug agents within an interior lumen so as to promote continued progressive growth of the proximal section of the transected nerve toward the distal section of the transected nerve;

FIG. 9 illustrates a partial cross-sectional view of another embodiment of a nerve repair conduit configured to provide a concentration gradient of one or more drug agents within the interior lumen so as to promote continued progressive growth of the proximal section of the transected nerve toward the distal section of the transected nerve; and

FIGS. 10 and 11 are graphs comparing performance of a nerve repair conduit in vitro and in vivo testing with predicted performance based on a functional model.

DETAILED DESCRIPTION I. Introduction and Definitions

The present disclosure relates to nerve repair conduits, kits that include such conduits, and methods for using such conduits. The nerve repair conduits described herein are configured for covering a damaged portion of a nerve and deliver one or more drugs thereto increase the rate of functional recovery. For example, with a transected nerve, the nerve repair conduits described herein may secure a proximal portion of the severed nerve in proximity to a distal portion of the severed nerve. The conduits described herein may, for example, be positioned around injured (e.g., crushed), partially transected, or fully transected nerves end-to-end, end-to-side, side-to-end or side-to-side. In addition, the nerve repair conduits described herein include drug reservoirs that are positioned on the conduits inside the body (i.e., in vivo) at the site of nerve repair without the use of an external drug conduit, thus (1) continuously delivering small molecules or growth factors to the adjoined nerves at a controlled rate and (2) improving the degree of axon regeneration and functional recovery. These nerve conduits are unique in that the desired drug(s) or other agents are released from an integrated (i.e., in situ) reservoir through an outlet (e.g., a semi-permeable membrane) into the conduit lumen in proximity to the injured nerve. This delivery configuration can allow for more controlled and uniform delivery of one or more compounds rather than relying on drugs embedded in biodegradable conduits or drugs that are administered from outside the body, which may have inconsistent delivery kinetics and significant burst effects.

Trauma patients with peripheral nerve injury suffer from life-long loss and/or disturbances in function mediated by the injured nerve. Nerve injuries with large gaps (>1 cm) require special bridging strategies for tension-free repair. Autologous nerve grafts (e.g., sural nerve or posterior interosseous nerve) serve as the current state-of-the-art in repairing such gaps, but numerous challenges associated with this approach results in functional benefits to only 40-50% patients. These include loss of sensation at the donor site, morbidity at the site of harvesting of donor nerve(s), limitations in the amount of nerve that can be harvested, mismatches in size and fascicular patterns between the nerve stumps and the graft, and the need for an additional surgical site. In recent years, grafts made from biologically derived materials have gained traction over allogenic and xenogenic tissues. Collagen, fibrin, and fibronectin have been used in addition to synthetic materials such as aliphatic polyesters and hydrogels. These hollow tubes act as axon guides for the regenerating nerves and can allow for tension free bridging without the need to harvest donor nerve. Separately, it has been shown that locally delivering growth factors or small molecules can enhance axon sprouting and peripheral nerve recovery. In animal models, NGF, VEGF, and GDNF delivered locally can act to direct axon growth, and/or enhance axon regeneration. Local delivery of growth factors has shown promise in recruiting nerve growth promoting cells like Schwann cells and endothelial cells and in promoting direct axon growth.

To address these issues, this disclosure relates to nerve conduits and methods for repairing injured, partially transected, or severed nerves (e.g., peripheral nerves) in a manner that facilitates healing of the of the nerve and improves patient outcomes. The nerve conduits are fabricated from a flexible, polymeric material and include a hollow annulus that serves as a guidance bridge for axons and nerve signaling molecules while a permeable outlet permits for delivery of an agent (e.g., a drug) into the annulus. The nerve repair conduits described herein are designed to continuously deliver the agent within the nerve conduit in the vicinity of the nerve repair at an essentially constant rate over an extended period of time (e.g., 1 week to 6 month) to improve the degree of nerve regeneration and functional recovery. The nerve repair conduits described herein can be used for cover injured portion(s) of nerves and/or adjoining partially transected or fully transected nerves in an end-to-end, end-to-side, side-to-end, or side-to-side fashion. The nerve conduits and the methods of their use disclosed herein have the potential to impact a broad spectrum of patients including those with nerve tumors, battlefield or other traumatic injuries and those with localized nerve inflammation.

Two components of this disclosure are: 1) nerve conduit design and 2) conduit implantation in vivo. Each of these components utilizes an innovative approach, which if successful, could fundamentally change the way peripheral nerve injuries are treated, resulting in improved outcomes and reduced disability for patients.

In one embodiment, a nerve repair conduit is disclosed. The nerve repair conduit includes a novel delivery apparatus integrated with a nerve guide conduit for delivering an agent (e.g., a drug) into the conduit. The nerve repair conduit includes a drug delivery reservoir that is attached to the nerve repair conduit. In other words, embodiments of the present disclosure may be used for nerve repair and delivery of an agent in vivo without relying on an exterior source of the source of the agent and without relying on integrating the agent directly into the material used to form the conduit.

The contents of the drug delivery reservoir (e.g., protein, small molecules, cells, nucleic acids, virus particles, etc. plus an optional excipient) are separated from the interior lumen of the conduit via an outlet (e.g., a semi-permeable membrane). The outlet is selected to allow for controlled delivery kinetics (e.g., near zero-order release kinetics or near first-order release kinetics) into the lumen of the conduit and where the agent can come into contact with and enhance growth of the regenerating nerve. In one embodiment, the device will be designed so the drug delivery reservoir does not extend all the way to the ends of the conduit. This will allow for sutures to be placed between the nerve epineurium and the conduit ends without puncturing the reservoir or membrane. This excess conduit length on either end can also be trimmed if necessary for tailored size match with the nerve gap.

Other groups have utilized hydrogels, fibrin, and polymer gels as carriers with growth factors and small molecules. These conjugated carriers were then filled into the lumen of nerve conduits as a means to locally deliver the proteins/molecules of interest. Attempts have also been made to incorporate drug into the biodegradable construct of the conduit itself. Each of these approaches has variable drug release kinetics. As the carrier or conduit construct itself biodegrades, there is often a burst of drug release that is neither sustained (i.e., not a constant rate) nor at the desired dose.

The devices and methods disclosed herein have the clear advantage of versatility of releasing a variety of different neurotrophic factors (e.g., proteins, small molecules, other neurotrophic factors, or combinations thereof) and/or other agents (e.g., cells, nucleic acids, viruses, anti-rejection drugs (e.g., steroids, cyclosporine, Prograf, etc.), or combinations thereof). That is, a variety of different drugs and/or other agents can be loaded into the drug release reservoirs of the nerve repair conduits described herein. In addition, the drug concentration, kinetics of delivery and duration of delivery can be readily adjusted by, for example, changing the size/volume of the drug release reservoirs, changing the excipient, changing the permeability or size of the outlet from the reservoirs, etc. Likewise, because the nerve repair conduits described herein can have more than one drug release reservoir, it is possible to tailor drug concentration, kinetics of delivery, duration of delivery, and/or elution rates independently. In addition, timing of release from different reservoirs can be tailored. For example, a first reservoir could be loaded with a drug that releases in the first 2 weeks and a second reservoir could be loaded with a drug that does not start to release until after 2 weeks.

For example, with the device described herein, the diffusion of each new drug can be titrated to near zero-order kinetics with iterative refinements of the outlet from the reservoirs with, for example, changes to the semi-permeable membrane pore size and surface area, reservoir size, and with the addition of a polymer matrix (e.g., polyvinyl alcohol (“PVA”), ethylene-vinyl acetate (“EVA”), hyaluronic acid, chitosan, PEG, poly-PNIPA, polyepsilon caprolactone-co-lactide-polyethylene glycol, HEMA, or a hydrogel) for controlled drug release. In one possible drug delivery scenario, the controlled release of a given drug may be driven by two separate mechanisms: (i) a semi permeable filter/membrane and (ii) a polymer matrix. This two-fold delivery mechanism can result in controlled delivery of multiple drugs and potentially tailor the release of individual drugs at different rates from the same device, thus allowing for simpler device customization. In addition, slow degradation of the matrix may prevent sudden release of drugs in the event of unlikely, but possible, unplanned leakage or puncture of the drug delivery device.

In addition to the foregoing, recent research into cell-based therapies has shown promise as a means to augment peripheral nerve repair. The devices described herein have the potential to function synergistically with stem cells, Schwann cell, and epithelial cell transplants by delivering proteins or growth factors to the nerve cells to direct differentiation or stimulate function. In one example, at least one portion of the interior lumen of the devices described herein may be coated with a layer of cells that can aid the nerve repair and growth. In another example, cells may be delivered into the interior lumen from a drug reservoir.

While nerve repair is generally the focus of the present disclosure, the device described herein could be used in a variety of tissue repair and localized drug delivery strategies. For example, devices described herein have the potential for broad applicability for healing tendon and bone or local anti-tumor therapies. Likewise, the conduits described herein could be installed around injured, diseased, or repaired blood vessels to deliver agents such as anticoagulants, or VEGF to enhance blood vessel healing or possibly deliver nitric oxide at an area of blood vessel stenosis to help dilate the vessel.

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings.

Although directional references, such as upper, lower, downward, upward, rearward, bottom, front, rear, etc., may be made herein in describing the drawings, these references are made relative to the drawings (as normally viewed) for convenience. These directions are not intended to be taken literally or limit the present invention in any form. In addition, terms such as “first,” “second,” and “third” are used herein for purposes of description and are not intended to indicate or imply relative importance or significance.

II. Nerve Repair Conduits

Referring now to FIG. 1A, one embodiment of a nerve repair conduit 100 is illustrated. The nerve repair conduit 100 includes a proximal end 102, a distal end 104, an exterior surface 106, and an interior surface 108 that defines an interior lumen. In addition, the nerve repair conduit 100 includes a first drug reservoir and a second drug reservoir schematically illustrated at 110 a and 110 b. The drug reservoirs 110 a and 110 b are attached to the outer surface 106 of the nerve repair conduit 100 such that drugs may be delivered into the interior lumen of the nerve repair conduit 100 via an outlet (e.g., a semipermeable membrane). The drug reservoirs 110 a and 110 b deliver drug to the interior lumen of the conduit 100 from a position inside the patient's body at the site of implantation of the nerve repair conduit 100. In other words, the drug and/or another agent is stored in and delivered from inside the body, not from a source outside the body. Likewise, the drug and/or another agent is stored in a reservoir and is not directly integrated into the polymer or another material used to form the conduit. In the embodiment illustrated in FIG. 1A, the drug reservoirs 110 a and 110 b may be sacs, bags, pouches, pods, bladders and the like. And while FIG. 1A illustrates two drug reservoirs 110 a and 110 b associated with the proximal 102 and distal 104 ends of the conduit 100, the number and positioning of the drug reservoirs may be changed without departing from the spirit of this disclosure.

Referring now to FIG. 1B, another embodiment of a nerve repair conduit 150 is illustrated. The nerve repair conduit 150 includes an inner tube 170 and an outer tube 172 that is disposed around the inner tube 170. The nerve repair conduit 150 includes a proximal end 152, a distal end 154, an exterior surface 156, and an interior surface 158 that defines an interior lumen. In addition, the nerve repair conduit 150 includes a drug reservoir 160 (i.e., the outer tube 172). The drug reservoir 160 is arranged as a concentric cylinder that surrounds at least a portion of the inner tube 170. The drug reservoir 160 is fluidly connected to the interior lumen of the inner tube 170 of the conduit 150 via an outlet (see, e.g., FIGS. 2A and 2B, elements 212 a and 212 b) such that drugs may be delivered into the interior lumen of the nerve repair conduit 150.

In one embodiment, the nerve repair conduit described herein may be configured to deliver the at least one drug at a substantially constant rate for at least 24 hours, one week, two weeks, three weeks, or four weeks or more (e.g., up to six months). Typically, the duration of delivery of the at least one drug is a function of one or more of a volume of the one or more reservoirs, the excipient, number of outlets, outlet size, or diffusion rate of the at least one drug through the at least one outlet. In another embodiment, the nerve repair conduit may be configured to deliver the at least one drug with, for example, substantially zero order kinetics or substantially first-order kinetics, for at least 2 weeks, three weeks, or four weeks.

As used herein, the terms “substantially zero order kinetics” or “zero order” refer to a process that has a rate that is independent of the concentration of the component(s). In diffusion, this, for example, may refer to process where the rate of diffusion of a species across a barrier (e.g., a semi-permeable membrane) is substantially independent of the concentration of the species on either side of the barrier. This may be accomplished, for example, by integrating the species into a matrix wherein the rate of diffusion is a function of the rate of release of the species from the matrix. As used herein, the terms “substantially first order kinetics” or “first order” refer to a process that has a rate that dependent on the concentration of only one component. Other components may be present, but each will be zero-order.

Referring now to FIGS. 2A and 2B, an end cut-away view and a side cut-away view of a nerve repair conduit 200 are illustrated. The nerve repair conduit 200 is similar to the embodiment of FIG. 1B except that they outer tube 222 is divided by a divider 224 that extends between the inner tube 220 and the outer tube 222 such that the outer tube 222 and the inner tube define a first reservoir 210 a and a second reservoir 210 b. While the divider 224 is shown as dividing the reservoir horizontally (i.e., oriented along the long axis of the nerve repair conduit 200), divider(s) (such as divider 225) may also be oriented orthogonal to the long axis of the nerve repair conduit 200 such that different reservoirs are positioned in different longitudinal sections of the nerve repair conduit 200. In another embodiment (not shown), reservoirs 210 a and 210 b may be further divided to form additional drug reservoirs. Outlets 212 a and 212 b are formed in the inner tube 220 forming a passageway between the drug reservoirs 210 a and 210 b, the exterior surface 206 of the conduit 200, and the interior surface 208 of the conduit 200. The outlets 212 a and 212 b allow for drug to diffuse from the drug reservoirs 210 a and 210 b into the interior lumen of the conduit 200. The diffusing drug is illustrated by arrows 214 a and 214 b.

As shown in FIG. 2B, it appears that outlets 212 a and 212 b are formed on or affixed to the inner surface 208 of the conduit 200. However, one will appreciate that the outlets 212 a and 212 b may be affixed to or formed on surface 206, or outlets 212 a and 212 b may be integrally formed on either surface 206 or 208. In one embodiment, the outlets 212 a and 212 b may be formed by affixing a semi-permeable membrane to the inner 208 or outer 206 surface of the conduit 200. The outlets 212 a and 212 b are configured to allow drug to diffuse from the drug reservoirs to the interior lumen of the conduit. In one embodiment, an outlet may have a nominal pore size of 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or larger depending in the application and the size of the drug that needs to diffuse through the outlet. Suitable examples of a semipermeable membranes having such pore sizes include, but are not limited to, polyether sulfone (“PES”), ethylene-vinyl acetate (“EVA”), PLGA, and other semipermeable membranes known on the art. In another embodiment, the outlets one 212 a and 212 b may be formed by forming holes (e.g., by laser cutting) that extend between the outer 206 and inner 208 surfaces. In addition to forming holes in the inner tube 222, the inner surface 208 may be etched (e.g., laser etching), scratched, or formed with longitudinal grooves that may act as guides for regenerating axons. The holes may be nano-scale holes, micro-scale holes, otherwise sized, or combinations thereof.

The nerve repair conduit 200 may have an interior D diameter of about 0.5 mm to about 2 cm, about 1 mm to about 1 cm, about 1 mm to about 5 mm, about 2 mm to about 4 mm, or about 2.5 mm to about 3 mm. For example, for repairing a typical peripheral nerve, a repair conduit having an inner diameter of about 1-2 mm may be sufficient. However, for repairing a major nerve (e.g., the sciatic nerve) and conduit having a size of 1-2 cm may be necessary.

The nerve repair conduits described herein (e.g., conduits 100, 150, and 200) may be fabricated from a polymeric material. In one embodiment, the polymeric material may be a flexible polymeric material. The nerve repair conduits described herein may be fabricated from biodegradable and/or non-biodegradable materials. Suitable examples of materials that can be used to fabricate the nerve repair conduits described herein include, but are not limited to, poly(lactic-co-glycolic acid) (“PLGA”), collagen, spun silk, electrospun silk, polytetrafluoroethylene (“PTFE”), polydimethylsiloxane (“PDMS”), silicone, a salicylic acid-based polymer, a salicylsalicylic acid-based polymer, a difluorophenyl-salicylic acid-based polymer, collagen, fibrin, fibronectin, alginate, gelatin, keratin, thrombin, poly-glycolic acid, poly-(lactic acid), poly-caprolactone, poly-(L-lactic acid), poly(3-hydroxybutyric acid), poly((bis(hydroxyethy) terephthalate-ethyl phosphoester/terephthaloyl chloride), poly(2-hydroxyethyl methacrylate) (“PHEMA”), a co-polymer of PHEMA and methyl methacrylate, poly(acrylonitrile-co-methylacrylate), and combinations thereof.

The nerve conduits described herein may be fabricated by a number of techniques. For example, the conduits described herein may be cast, injection molded, or micromachined (e.g., by xurography or laser). In one example, the inner tube 220 of the conduit 200 may be fabricated by dissolving the polymer (e.g., PLGA) in a compatible solvent (e.g., acetone) and then casting the inner tube 220 in a glass capillary tube. As the solvent evaporates, the polymer clings to the walls of the capillary and an interior lumen is formed by evaporation of the solvent. Once the solvent has evaporated, the annular inner tube 220 may be recovered by breaking the glass mold. The outlet(s) may be formed by cutting one or more holes (i.e., windows) in the inner tube 220 and affixing a semipermeable membrane over the hole. For example, the semipermeable membrane may be affixed to the inner tube with glue. In another embodiment, the outlet(s) may be formed by laser cutting holes in the inner tube. The holes may include nano-scale holes, micro-scale holes, other holes, or combinations thereof. In another example, the outlet(s) may be formed by biodegradation of the inner tube 220 of the conduit 200. In yet another example, the outlet(s) may be formed by adjusting the polymer makeup of the material used to form the inner tube such that the drug(s) can diffuse directly through the wall of the inner tube into the interior lumen of the conduit.

The outer tube 222 (i.e., the drug reservoir tube) may be fabricated in a similar fashion, except a larger capillary tube may be used to obtain the larger diameter of the outer tube 222. The reservoir 210 may formed be by arranging the outer tube 222 around the inner tube 220 and sealing the open ends of the outer tube 222. The open ends of the outer tube may be sealed with, for example, glue or plugs. Once formed, the reservoir may be filled by injecting drug(s) and an optional excipient (e.g., PVA) into the reservoir with, for example, a hypodermic needle. The hole formed in the reservoir may be sealed with a drop of glue or polymer (e.g., PLGA).

Suitable examples of agents that may be used in the reservoir(s) include, but are not limited to, neurotrophic factors, pain medications (e.g., opioids), antirejection drugs (e.g., glucocorticoids), antimicrobials, nerve stimulating drugs (e.g., agrin), NSAIDs, small molecule drugs (e.g., epoxy eicosanoids), nucleic acids (e.g., DNA or RNA), viruses carrying nucleic acids for transfection of cells in around the nerve. and the like. In addition, the reservoir(s) may be loaded with cells (e.g., Schwann cells or adipose derived stem cells), and cells that release growth factors or cytokines, or combinations thereof. Suitable examples of neurotrophic factors include one or more of nerve growth factor (“NGF”), glial cell-derived neurotrophic factor (“GDNF”), vascular endothelial growth factor (“VEGF”), netrtin-1, or fibroblast growth factor (“FGF”).

In one embodiment, where multiple reservoirs are filled with different agents, the separate agents may have at least one of different release rates, different durations of release, different release times, or different release locations in the interior lumen. For example, different release rates, different release times, and different release locations in the interior lumen may be accomplished by using different semipermeable membranes, different membrane areas, different excipients, and/or different outlet locations.

In addition to infusing the interior lumen with drug agents, the inner surface 208 of the conduit 200 may be coated with cells that may aid nerve healing or repair. In one embodiment, the interior lumen of the conduit 200 may be lined with one or more of Schwann cells, stem cells or blast cells (e.g., adipose derived stem cells, mesenchymal stem cells, bone marrow derived stem cells, neural tube lineage cells, etc.), or epithelial cells. Cells such as Schwann cells, stem cells, and blast cells may, for example, provide molecular factors that aid nerve healing and repair while epithelial cells may, for example, help with revascularization of the tissue surrounding the repair site.

Referring now to FIGS. 3A and 3B, a side elevation view of a nerve repair conduit adjoining a transected nerve in an end-to-end fashion and a partial cut-away view of a nerve repair conduit adjoining the transected nerve are shown. The nerve includes a proximal section 316 and a distal section 320. The nerve repair conduit 300 includes a proximal end 302, a distal end 304, an exterior surface 306, an interior surface 308 that defines an interior lumen, and a drug reservoir 310. A drug outlet 312 is shown on the interior surface 308 of the conduit 300. The proximal end 318 and the distal end 322 of the nerve are placed into proximity to one another in the interior lumen. Diffusion of the drug out of the outlet 312 into proximity of the proximal end 318 and the distal end 322 of the nerve is shown at 314.

Referring now to FIG. 3C, a partial cut-away view of a nerve repair conduit 350 adjoining a transected nerve in a side-to-side fashion is schematically illustrated. The principle of operation of the nerve repair conduit 350 is similar to the nerve repair conduit 300 described in FIGS. 3A and 3B. The nerve repair conduit 350 includes an open proximal end 351, a closed distal end 352, and a drug reservoir 354. The nerve includes a first portion 356 and a second portion 360. The nerve ends 358 and 362 are each positioned within the conduit and may be secured to one another by one or more sutures (not shown). The nerve repair conduit 350 may be secured to either or both of the nerve ends 358 and 362 with one or more sutures (not shown). As in the previous examples, the drug reservoir 354 may be loaded with one or more agents that can be delivered into the vicinity of the nerve ends 358 and 362 to speed/improve healing, improve patient outcomes, and the like. Additional discussion of side-to-side nerve repair can be found in U.S. patent application Ser. No. 13/200,028, the entirety of which is incorporated herein by reference.

Referring now to FIG. 4, a partial cut-away view of an alternate embodiment of a nerve repair conduit 400 that includes a nerve graft 424 for adjoining a transected is illustrated. Typically, the nerve conduits shown in FIGS. 3A and 3B are only able to repair nerves with a gap of about 2-3 cm. For injured nerves with larger gaps (e.g., larger than about 2-3 cm), a nerve graft can serve as a bridge. The nerve repair conduit 400 includes a proximal end 402, a distal end 404, an exterior surface 406, an interior surface 408 that defines an interior lumen, and a drug reservoir 410. The nerve repair conduit 400 includes a number of drug outlets 412 a, 412 b, and 412 c.

The nerve conduit 400 includes a nerve graft 424. The transected nerve includes a proximal end 416 and a distal end 420. The nerve conduit 400 includes a nerve graft 424. The first end of the nerve 418 and the second end of the nerve 422 and bridged by the nerve graft. In one embodiment, the nerve graft 424 may be an autograft harvested from the patient. In another embodiment, the nerve graft 424 may be an allograft. For example, an allograft may be harvested from a cadaver. Where the graft 424 is an allograft, xenograft, or a decellularized graft, the reservoir 410 may, for example, include at least one anti-rejection drug selected to prevent rejection of the graft.

In some embodiments, a nerve repair conduit is configured to provide a gradient concentration of one or more drug agents across the longitudinal length of the interior lumen. In use, such embodiments can function to beneficially encourage the continued growth of nerve axons from the proximal section of a transected nerve toward the opposite distal section of the transected nerve. By providing a gradient concentration that progressively increases the concentration of drug agent from the end of the proximal nerve section to the distal nerve section, the end of the regenerating proximal section can be continuously encouraged to “reach” farther distally to areas of higher concentration of drug agent. This can thereby promote the faster and/or more effective joining of the proximal nerve section to the distal nerve section.

The beneficial concentration gradient may be provided as a result of the particular configuration of outlet(s) (e.g., holes and/or membranes) formed between the reservoir and the interior lumen of the device. Outlet configurations (i.e., the particular size and/or spacing of outlets for a given device or section of a device) may sometimes be referred to herein as an “outlet arrangement.”

It is noted that while the terms “proximal nerve section” and “distal nerve section” are used for convenience to distinguish between different sections of the nerve for which repair is sought, the use of these terms does not necessarily correlate to macro level anatomical use of the terms proximal and distal. That is, use of these terms does not necessarily require that the growing portion of the nerve (referred to herein as the proximal section) actually be anatomically proximal of the non-growing portion of the nerve (referred to herein as the distal section). It will therefore be understood that the concentration-gradient-based embodiments described herein may be oriented so that the concentration gradient promotes continued growth of the growing end of the nerve toward the non-growing end of the nerve, regardless of the actual proximal/distal anatomical orientation of the nerve for which repair is sought.

FIGS. 7A through 7C schematically illustrate typical progressive growth of a proximal nerve section 516 toward a distal nerve section 520 within an interior lumen 528 of a polymeric body of a nerve repair conduit 500. As shown, the nerve ending 518 of the proximal nerve section 516 regenerates and moves distally toward the nerve ending 522 of the distal nerve section 520, as indicated by arrow 515. Because of the unidirectional manner in which nerves function and grow, the distal nerve section 520 will typically not grow proximally toward the proximal section 516. Connection of the nerve therefore depends on promoting regeneration and growth of the proximal nerve section 516 along the direction indicated by arrow 515. As described in more detail below, certain nerve repair conduit embodiments include features that enable the reservoir 510 to provide one or more drug agents to the interior lumen 528 with a longitudinal concentration gradient that increases in concentration from the proximal side of the device to the distal side.

FIG. 8 illustrates one embodiment of a nerve repair conduit 600 configured to provide such a longitudinal concentration gradient. The embodiment shown in FIG. 8 may be utilized to beneficially promote continued growth of the proximal nerve section 616 toward the distal nerve section 620. As shown, the nerve repair conduit 600 includes a hole 613 (i.e., outlet) for providing fluid communication between the reservoir 610 and the interior lumen 628 of the device. The hole 613 is located so that diffusion of one more drug agents leads to relatively lower concentration levels in the proximal section 627 of the lumen and relatively higher concentration levels in the distal section 629 of the lumen. Because the drug agent has a greater longitudinal distance to cover when diffusing proximally, the resulting concentration gradient will progressively increase in the distal direction.

The size of the hole 613 may be tailored so that the drug(s) of interest sufficiently diffuse to the proximal section 627 to reach the nerve ending 618. This encourages regenerative growth of the nerve ending 618 in the distal direction. Because the concentration gradient within the interior lumen 628 progressively increases, the nerve ending 618 will continually be encouraged to grow further distally toward the areas of higher concentration. Where no concentration gradient is supplied, nerve repair may be slowed or otherwise hindered. For example, without progressively higher concentration levels in the distal direction, a growing nerve ending may stop or slow its distal growth. In contrast, the longitudinal concentration gradient provided by embodiments such as shown in FIG. 8 encourages continuous growth of the nerve ending 618 so that it can more effectively reach the opposite nerve ending 622 of the distal nerve section 620.

To provide the concentration gradient, the hole 613 is placed at a position that is closer to a distal end of the interior lumen 628 than a proximal end of the interior lumen 628. For example, for a given length of the interior lumen 628, the hole 613 may be placed at a position located at about 55% to about 95% of the length of the lumen 628 from the proximal end. More preferably, the hole 613 is placed at a position located at about 60% to about 80% of the length of the lumen 628 from the proximal end. These hole positions beneficially allow for sufficient diffusion of the drug agent(s) to the proximal end of the lumen while also providing effective concentration gradients to promote continued distal nerve growth.

FIG. 9 illustrates another embodiment of a nerve repair device 700 configured to provide a longitudinal concentration gradient within the interior lumen 728. The nerve repair device 700 includes multiple holes 713 a, 713 b, 713 c (collectively referred to as holes 713). Though three holes are shown here, it will be understood that this is provided as an exemplary embodiment, and other embodiments may include other numbers of holes (e.g., two holes or more than three holes). The holes 713 are configured in size and relative orientation to provide a longitudinal concentration gradient with lower concentration levels in the proximal section 727 of the lumen transitioning to higher levels in the distal section 729 of the lumen.

As shown, the holes 713 are differentially sized and are arranged with progressively larger holes located closer to the distal end of the device. This configuration can beneficially supply sufficient overall levels of drug agent(s) from the reservoir 710 into the interior lumen 728 while also providing a longitudinal concentration gradient that increases in the distal direction. In the illustrated embodiment, the hole 713 a is located proximally and is relatively small, the next hole 713 b is somewhat larger, and the next hole 713 c is larger still. In other embodiments, each successive hole need not necessarily be larger than the previous hole, though preferably the overall trend is for more distal sections to include a greater average hole size that more proximal sections.

Other embodiments of nerve repair devices may include additional or alternative configurations of outlets or holes for providing a concentration gradient. For example, some embodiments may include multiple holes such as in the embodiment of FIG. 9, but with a general trend toward increasing hole density (i.e., number of holes per a given area) in the distal direction. Increasing hole density may be utilized in addition to or as an alternative to increasing hole size for providing a concentration gradient.

In general, a gradient may be provided by defining an intermediate point on the nerve repair device somewhere between the proximal and distal ends of the device (e.g., near the longitudinal midpoint of the device), and then configuring the device so that a section distal of the intermediate point has a greater overall hole surface area for transfer of drug agent(s) as compared to a section of the same size proximal of the intermediate point. This differential in available hole surface area may be provided by adjusting the size and/or number of holes in the different sections.

Hole sizes can vary according to anatomical conditions, treatment requirements, drug(s) to be delivered, nerve gap size, and other application variables. In a typical application, by way of example, hole sizes may range from about 50 μm to about 150 μm, or more typically from about 60 μm to about 120 μm, though different sizes may be utilized according to particular application needs. It will also be appreciated that though “holes” are used in some of the examples described herein, that membranes and/or other structures may also be used so long as they are capable of permitting the transfer of drug agent(s) from the reservoir to the interior lumen of the device. Thus, a “hole” as used herein need not necessarily be completely open so long as it is configured to provide the function of transferring drug agent(s) from the reservoir to the interior lumen.

In embodiments having multiple holes, the holes may be arranged so as to be substantially longitudinally aligned along the polymeric body. Alternatively, the multiple holes may be placed out of longitudinal alignment. For example, some embodiments may position the multiples holes in a spiral arrangement around the circumference of the polymeric body. Such non-aligned embodiments may beneficially aid in better circumferentially distributing the drug(s) passing from the reservoir into the interior lumen of the polymeric body.

Some embodiments may combine one or more of the above-described gradient-enabling features with one or more reservoir dividers also as described above. For example, a reservoir may include one or more longitudinally oriented dividers that divide the reservoir into two or more separate sections each extending the longitudinal length of the reservoir. One or more of the separate reservoir sections may include a hole arrangement for providing a longitudinal concentration gradient. Such embodiments can beneficially provide separate concentration gradients of separate drugs or combinations of drugs each loaded into a respective separate longitudinal reservoir section. Some embodiments may include one or more orthogonal dividers with one or more of the resulting reservoir sections including a gradient-forming hole arrangement. Even though such reservoir sections do not extend the entire longitudinal length of the polymeric body, they may still be configured to provide a concentration gradient within the sub-portion of the longitudinal length they cover.

III. Methods of Nerve Repair

In one embodiment, a method for repairing a nerve is disclosed. The method includes (1) providing a nerve repair conduit as described above, (2) securing the proximal end of the nerve repair conduit on a first portion of a nerve and securing the distal end of the nerve repair conduit on a second portion of a nerve such that the first and second portions are in fluid communication with one another via the interior lumen of the nerve repair conduit, and (3) infusing the first and second portions with at least one agent from the one or more drug reservoirs that are associated with the conduit. The first and second portions may, for example, include proximal and distal portions of an injured but still intact nerve (e.g., a crushed nerved), or the first and second portions may include proximal and distal portions of a partially or fully transected nerve.

In one embodiment, the at least one agent may be delivered at a rate having substantially controlled kinetics (e.g., substantially zero-order or substantially first-order kinetics and over an extended period of time—e.g., at least one week, two weeks, three weeks, at least one month, or longer. In another embodiment, the at least one agent may be delivered at a substantially constant rate over an extended period of time—e.g., at least 24 hours, one week, two weeks, three weeks, at least one month, or longer.

In one embodiment, the first and second nerves may be connected end-to-end. In another embodiment the first and second nerves may be connected side-to-side. The first and second nerves may include proximal and distal segments of a transected or partially transected peripheral motor or sensory nerve.

In a specific embodiment, the nerve repair method described herein may include positioning a nerve graft in the nerve repair conduit and securing the proximal end of the nerve repair conduit on the selected portion of the first nerve and securing the distal end of the nerve repair conduit on the selected portion of the second nerve such that the nerve graft acts as a bridge between the first and second nerves.

In one embodiment, the nerve graft may be an allograft. If an allograft, xenograft, or a decellularized graft is used, the method may further include infusing the nerve graft with at least one anti-rejection drug from the one or more drug reservoirs in order to prevent rejection of the graft.

IV. Examples Example 1—PLGA-BSA Release/Leakage Test

A 7-day release/leakage test was performed in order to explore the capacity of the PLGA device to deliver drugs of interest. Bovine serum albumin (BSA) was chosen to serve as the drug because its size is bigger than most of the growth factors. Two samples filled with 30 μL 300 mg/mL BSA were tested with two negative controls, two leakage test samples and a positive control, as shown in Table 1.

TABLE 1 List of samples involved in the PLGA-BSA release/leakage test Protein in the Receiver Sample Name Purpose Reservoir Reservoir chamber Positive Control The maximum possible n/a 42 uL 300 mg/mL 7.5 mL PBS (PC) est. conc. conc. in the receiver BSA directly (tween free) 1800 ug/mL chamber. injected into the *Note: use Use design's dimension: PBS 7 mL Amber max 42 uL drug reservoir Glass Vial volume. Leakage Test 1 To test if no BSA is #1 30 uL 300 mg/ml 7.5 mL PBS (LT1) detected when using a BSA device filled with BSA and without window & filter. Leakage Test 1 Duplicate LT1 #2 30 uL 300 mg/ml 7.5 mL PBS (LT2) BSA (duplicate LT1) Negative To test the device without #3 30 uL PBS 7.5 mL PBS Control 1 BSA and with filter& (NC1) window will show no BSA in the receiver chamber. Negative Duplicate NC1 #4 30 uL PBS 7.5 mL PBS Control 2 (NC2) (duplicate NC1) Sample 1 Sample of interest. with #5 30 uL 300 mg/mL 7.5 mL PBS device, with window, BSA with BSA Sample 2 Another sample. #6 30 uL 300 mg/mL 7.5 mL PBS Exactly the same as BSA Sample 1.

BSA concentrations in the receiver chamber of each vial were obtained from the calibration equation generated from the plate reader. Cumulative BSA release into the receiver chamber and the percentage release of BSA in the receiver chamber were plotted based on the BSA concentration values. FIGS. 5 and 6 show the result in micrograms and percent, respectively.

For the leakage test, one of the two samples (LT1 and LT2) leaked through the side of the PLGA outer tube when filling BSA into the reservoir, and therefore LT2 shows a signal raising in both FIGS. 5 and 6. On the other hand, LT1 shows no leakage and no noticeable BSA release was detected in the receiver chamber.

For the release test, Sample 1 has a rapid release (64.8%) in the first 24 hours and slowed down in the next 6-day period. Sample 2, on the other hand, released BSA promptly in the first 4 hours (13.7%) and showed a constant release rate for the rest of the time.

For future application, growth factors that can promote axon growth may be filled into the drug reservoir with polyvinyl alcohol (PVA) to control the release kinetics, if slower release rate is preferred.

Example 2—Long-Term Placement of PLGA Repair Conduits

PLGA conduits with drug reservoirs were used to repair transected nerves in an end-to-end and a side-to-side fashion in a mouse sciatic nerve model in order to determine whether biodegradation of PLGA causes an adverse reaction. Walking track analysis was performed every two weeks until animals were sacrificed at day 90. It was found that long-term placement of PLGA conduits and biodegradation of PLGA produced no adverse reaction. In general, side-to-side repair seemed to show some advantages, but side-to-side repair is not always an option if there is a nerve gap. However, it is expected that all repair outcomes (e.g., side-to-side, end-to-end, side-to-end, etc.) can be improved with the drug-delivering conduits described herein.

Example 3—Long-Term Animal Testing

The drug delivery conduits described herein are tested in a mouse sciatic nerve model. NGF and GDNF are two of many growth factors implicated in improved peripheral nerve regeneration and are the test drugs for these experiments as they have been shown to enhance nerve growth both in vitro and in vivo. The mouse sciatic nerve has been established as a viable model for evaluation of peripheral nerve injury because of its easy accessibility and reasonable size for testing. It is hypothesized that the novel strategy described herein will provide results superior to nerve conduit alone (without drug) and will approach the results of autologous nerve graft. The device is used in combination with an autologous nerve graft and it is hypothesized that this combination will provide superior results to autologous nerve graft alone.

Experimental design: This efficacy study utilizes a mouse sciatic nerve gap (10 mm) model using transgenic mice that express GFP (green fluorescent protein) only in their peripheral nerves (Jackson Laboratories). The following groups are included: Group 1 (n=16): sham transection; Group 2 (n=16): transection with no repair of the 10 mm gap; Group 3 (n=16): transection followed by interposition with an autologous nerve graft; Group 4 (n=16): transection followed by interposition with an empty PLGA conduit; Group 5 (n=16): transection followed by interposition with a PLGA conduit and NGF; Group 6 (n=16): transection followed by interposition with a PLGA conduit and GDNF; Group 7 (n=16): transection followed by interposition with a PLGA conduit along with NFG and GDNF; Group 8 (n=16): transection followed by interposition with autologous nerve graft surrounded with PLGA nerve guide and NGF; Group 9 (n=16): transection followed by interposition with autologous nerve graft surrounded with PLGA nerve guide and GDNF; Group 10 (n=16): transection followed by interposition with autologous nerve graft surrounded with PLGA nerve guide and NGF and GDNF. NGF and GDNF loading dosages are based on optimal concentrations from Aim 2.

Surgery: Prior to surgery the mice are anesthetized using isoflurane. The surgical area is shaved and prepared with betadine. A longitudinal incision is then made in the posterior distal thigh of the hind limb, separating the natural plane between the vertebral head of the biceps femoris and superior gluteal muscles. Under the operating microscope, a 1 cm segment of the sciatic nerve is isolated. For Groups 2-10 the sciatic nerve is transected to produce a 10 mm gap. For Groups 3 and 8-10 (autologous), the nerve segment removed during the transection is then reversed and reattached with epineural sutures in an end-to-end fashion. For the other groups the same sciatic nerve gap is created but the gap is bridged with a conduit. For Groups 8-10, the device is slid onto the transected nerve end and the nerve graft is then sutured in place. Once the graft is in place, the device is slid over the graft and the two repair sites are secured with sutures from epineurium to the device. It should be noted that the reservoir will not extend all the way to the edge of the conduit. There is a cuff of conduit on each end of the device, which serves as sites where sutures are placed to anchor the device. Half of the animals in each group (n=8/group) are sacrificed at 30 days and the other half at 90 days. The walking track, conduit, motor endplate, retrograde labeling, and gastrocnemius muscle atrophy are evaluated at 30 and 90 days.

Walking Track: Preoperatively and every two weeks after surgery a functional assessment of the animals' gait is performed. Briefly, the mouse's hind feet are pressed on an inkpad before walking along an 8×52 cm track. The sciatic, tibial, and peroneal functional indices are then calculated based on paw print measurements. These indices provide a gross estimate of major muscle group functional status.

Conduit Evaluation: The conduit is initially evaluated for the volume of NGF and GDNF remaining in the reservoir, the presence of any leaks, and the amount of each drug in the surrounding tissue and serum using commercially available ELISAs. The sciatic nerve inclusive of the conduit is then harvested, fixed in formalin, embedded in paraffin, and sectioned. Fluorescent microscopy is used to assess nerve growth into the conduit, since the transgenic mouse nerves express GFP. Slides are also be stained with H&E, S-100, PGP 9.5 and CD31. The different stains and fluorescent imaging are used to assess axon growth (number, diameter, and density), Schwann cell density, and blood vessel density within the conduit. Additionally, the conduit is evaluated for degree of degradation and the surrounding tissue evaluated for reaction to the presence of the conduit.

Motor Endplate Evaluation: The tibialis anterior muscle is stained en bloc with alpha-bungarotixin conjugated to Alexa 594 (Molecular Probes, OR) to label the acetylcholine receptors, DAPI to identify nuclei, and the nerves themselves already express GFP. The whole mounts are imaged using confocal microscopy by merging and flattening a stack of images taken 5 μM apart. Multiple images are evaluated for the percentage of re-innervated neuromuscular junctions.

Retrograde Labeling: The gastrocnemius of the anesthetized animals is injected with Fast Blue (Polysciences, Warrington, PN) six days prior to necropsy. At necropsy, the animal is perfused and the spinal cord at L2-L4 is harvested, placed in cold cryoprotective media, frozen in OTC compound, and sectioned (20-30 μM). The sections are examined by fluorescent microscopy to determine labeled motor neuron density.

Gastrocnemius Muscle: The gastrocnemius of both legs are harvested at necropsy being careful to dissect at the tendinous origin and insertion. The muscles are weighed and the degree of atrophy of the experimental leg calculated both in terms of absolute (grams) and relative atrophy [(experimental−control)/control*100)]. Additionally, the nuclear density of the gastrocnemius is obtained on H&E stained slides.

Electrophysiology: Sciatic nerve and muscle function are examined immediately prior to animals' sacrifice at 90 days. These studies are only performed on the 90 day groups. To assay motor function, the sciatic nerve proximal to the nerve transection is stimulated to record evoked muscle compound action potentials (mCAPs) in the plantar flexor (e.g., gastrocnemius) and dorsiflexors (e.g., tibialis anterior) muscles, and possibly nerve compound action potentials (nCAPs) distal to the transection (e.g., on tibial and peroneal branches). To assay sensory function, nCAPs proximal to the transection evoked by distal sensory stimulation are recorded. Metrics include size and conduction velocity of CAPs on the transected and contralateral side and are compared across experimental groups.

Anticipated results: It is anticipated that better outcomes will be observed, as determined by greater improvements to sciatic functional behavioral and physiological indexes, greater nerve in-growth into the conduit, and less gastrocnemius atrophy in the groups that are treated with our novel conduit-drug delivery device with NGF and/or GDNF compared to control groups. It is anticipated that the combined autologous nerve and drug-filled conduit group will show the best results. This may provide insight into a novel paradigm for treating peripheral nerve gaps with both autologous nerve and drug delivery as a means to further improve outcomes.

Example 4—Drug Release Diffusion Model

A mathematical model was developed to determine the device parameters such as hole size/number and loading concentration to obtain the desired in vivo concentration of interest, i.e. the internal instantaneous drug concentration within the guidance conduit.

The concept of using basic diffusion from a reservoir as the primary mode of drug release has been relatively unexplored for treatment of peripheral nerve injuries. Diffusion behavior is driven by Fick's laws of diffusion: Fick's 1^(st) law relates a particle's diffusive flux to its concentration difference:

$\begin{matrix} {J = {{- D}\frac{\Delta\; c}{\Delta\; l}}} & \left( {{Equation}\mspace{14mu} 1} \right) \end{matrix}$ where J is the diffusive flux

$\left( \frac{ng}{{cm}^{2}*s} \right),$ D is the diffusion coefficient, Δc is the difference in drug concentration, and l is the distance between the concentration difference.

Using Fick's law, a numerical model based on diffusion through the reservoir holes into the lumen of the conduit was developed to predict likely drug release from the device. MATLAB was used to implement the models. The model was constructed by simplifying the conduit into four distinct regions: a uniform drug reservoir, the diffusion hole, the inner conduit, and outside the conduit. Focused on these locations, a multi-step implementation of Fick's law was used to calculate the concentration at each region boundary and a cumulative mass release could be extracted. The model assumes one-dimensional diffusion and the reservoir was considered to have a homogenous concentration always with no fluid flow within the device. Another assumption was that the nerve conduit remains a fixed geometry device through its release cycle. For the nerve conduit, the drug release rate depends on the diffusion coefficient and the geometry of the device. As cross-sectional areas are decreased, the diffusion rate within each region is linearly decreased. Consequently, the conduit diameter and diffusion hole diameter will modify the diffusion rates in a quadratic manner. As the length of the inner conduit and wall thickness are increased, the diffusion rates through each of their regions linearly decreases. Finally, the mass of drug available in the reservoir does not affect the relative diffusion rate, but it does linearly scale the actual flux or mass that is delivered. Diffusion hole size and the initial reservoir concentration are the simplest variables that can be adapted to compensate for the rate of diffusion of each drug and the conduit size required.

Four diffusion areas/stages were assigned as follows: stage 1 is the drug reservoir filled with the desired drug; stage 2 is the area in the inner conduit near the diffusion hole; stage 3 is the area in the inner conduit at the boundary of the proximal/distal nerve stump; stage 4 is inside the proximal nerve stump where the drug undergoes diffusion through the nerve tissue in order to exert its therapeutic effect and stage 5 is a certain fixed distance (2 cm inside the nerve) where the drug is all consumed (acting as a sink).

The diffusion model was constructed to understand the change in drug diffusion in the conduit lumen due to changes in hole location, reservoir volume, and loaded drug concentration over a period of 30 days. As the location of the hole changes, the resistance experienced by the drug to reach the nerve end changes as well, which will have an impact on the gradient established inside the inner conduit. Similarly, changing the number of holes and the concentration of loaded drug will impact the drug concentration in the inner conduit lumen.

Combining Fick's first law (Equation 1) and second law of diffusion (Equation 2)

$\begin{matrix} {\frac{\Delta\; c}{\Delta\; t} = {D\frac{\Delta^{2}c}{\Delta\; l^{2}}}} & \left( {{Equation}\mspace{14mu} 2} \right) \end{matrix}$ gives the concentration change as a function of time. With this, the concentration at the various stages in the drug delivering conduit can be calculated.

The diffusion flux between stages 1-2, 2-3, 3-4 and 4-5 is J₁₋₂, J₂₋₃, J₃₋₄ and J₄₋₅ respectively; the area for the diffusion hole, inner conduit transverse cross-sectional area, and proximal nerve stump transverse cross-sectional area is A₁₋₂, A₂₋₃, A₃₋₄ and A₄₋₅, respectively; the concentration at stages 1, 2, 3, 4 and 5 is C₁, C₂, C₃, C₄ and C₅, respectively; the distance between stages 1-2, 2-3, 3-4 and 4-5 is l₁₂, l₂₃, l₃₄ and l₄₅, respectively.

We can obtain the stage diffusion equations as:

$J_{12} = {{- D}\frac{c_{1} - c_{2}}{l_{12}}}$ $J_{23} = {{- D}\frac{c_{2} - c_{3}}{l_{23}}}$ $J_{34} = {{- D_{n}}\frac{c_{3} - c_{4}}{l_{34}}}$ $J_{45} = {{- D_{n}}\frac{c_{4} - c_{5}}{l_{45}}}$

Assuming that the diffusion mass flow is the same in stages 1-2, 2-3, 3-4 and 4-5 we get: J₁₂A₁₂=J₂₃A₂₃=J₃₄A₃₄=J₄₅A₄₅

Based on our prior results, a C₃ value of 1-20 ng/mL for NGF and a J₁₋₂A₁₋₂ value of 0.1-25 ng/day for NGF are preferred. A starting concentration of C₁ and the diffusion hole size and number can be entered as boundary conditions for the equations above. This model was used to calculate the released drug using a step size of one minute in a 30-day period, and the drug released in each previous step was deducted from the drug reservoir. Using the values C₁-C₃, we evaluated C₄ (drug concentration diffused in the nerve). Following diffusion through the hole and into the conduit lumen; a concentration range is established from the hole to the nerve stump inserted in the conduit. For the mathematical model, we assume that the nerve fiber comprises a single homogeneous layer exhibiting isotropic diffusion properties. Within the tissue, the free drug (c₃) undergoes diffusion and finally, to exert its therapeutic effect, the free drug binds to binding sites or receptors and is consumed.

Example 5—Device Variation Using the Diffusion Model

Drug diffusion was modeled to understand how alteration to certain design parameters, such as the number and location of the diffusion holes, impacts the drug concentration within the lumen of the conduit. We used different values for drug loading concentration in the reservoir (0.05, 0.1, and 0.2 μg/ml), hole position from the proximal end (2, 3, and 7 mm), reservoir volume (10 and 20 μl), and number of holes (2 and 3). The primary objective was to calculate how concentration changes across the length of the conduit and determine if the selected parameters result in a therapeutic drug concentration within the device lumen. For this design evaluation task, we varied the different device parameters for a mouse sized single reservoir device delivering NGF.

Hole location: There was variation in the diffused drug concentration with changing hole locations. The highest (steepest) gradient of 0.6% per 100 um was produced by placing the hole at 7 mm from the proximal end of the device. Finally, the drug released out of the device was maintained within a therapeutic range of ˜5-7 ng/ml/day.

Reservoir volume: There weren't any significant differences in the diffused drug concentration range with changing reservoir volume. There was <1% change in the concentration range as the reservoir volume was changed from 10 to 20 ul. The difference in drug diffusion due to change in reservoir volume was compared across different hole locations and it was observed that there was <1% variation in the concentration of drug released inside the conduit. Devices with a reservoir volume of 10 ul released drug in a concentration range of ˜5-7 ng/ml/day; while the devices with the reservoir volume of 20 ul released drug in a concentration range of ˜5.5-7.5 ng/ml/day.

Drug Loading Concentration: It was observed that by changing reservoir concentration, the released drug concentration could be linearly scaled based on the concentration of drug in the reservoir. This linear scaling was repeatable across different hole locations as well. The total drug released from the device loaded with 0.2 ug/ml of drug was within the range of ˜9-15 ng/ml/day (FIG. 5 left); while the drug released from devices loaded with 0.05 ug/ml of drug was within the range of ˜2.5-4 ng/ml/day.

Number of holes: Changing the number of holes in increasing order of their size or adding holes created variable drug concentration ranges in the inner conduit. Two exemplary designs developed using the mathematical model that will produce varying concentration gradients within the device are: 1) 0.3% per 100 μm with two diffusion holes with the distal hole (90 μm) being larger than the proximal (60 μm) and 2) 0.1% per 100 μm with three progressively increasing sized diffusion holes from the proximal to distal end of the device (sized at 40 μm, 65 μm, 85 μm, respectively). While each of these designs produced a different range of concentration within the device, the total amount of drug released was consistent between devices. Hence, the model can be used to adjust concentration range inside the conduit to create a variety of gradients while maintaining the total drug released from the device.

Example 6—Microfluidic Device for Validating the Diffusion Model

A microfluidic device was built to validate that the drug diffusion matches the predictions based on our mathematical diffusion model. uFD devices were created by assembly of lasered acrylic sheets (thickness 0.5 mm) as shown in FIG. 7. The reservoir and channel shapes were created in the acrylic sheets and holes were made in a plastic sheet (150 um thick) using a VLS3.60 CO2 laser system (Universal Laser Systems), the same technique we utilized to manufacture the diffusion hole in our nerve guides [16]. The dimensions of the reservoir were 8 mm×2.5 mm to contain a total volume of 10 ul (same as the reservoir volume of our drug delivering conduit) and channel dimensions were 10 mm×1.2 mm to contain a total volume of 6 ul (same as the volume of our drug delivering conduit). The uFD was set up such that the plastic sheet containing the holes is placed between the reservoir and the channel; allowing for drug diffusion only through the holes (FIG. 7). Bonding of the layers containing reservoir and channel and the holes in the middle plastic sheet was done using double sided tape. The reservoir in FIG. 7 is filled with a red dye, for ease of viewing the different components of the device; the opaque tape that separates the reservoir and inner conduit was not applied. The OD device was used to validate the mathematical diffusion model.

The diffusion profiles from different μFD configurations were tested using a fluorescent dye (FITC-Dextran; similar molecular weight and diffusion coefficient as NGF or FK506). The height of the microfluidic channels was kept constant between the devices at 150 μm. Diffusion characteristics of the devices were examined by filling the reservoir of the devices with the fluorescent dye and channel with PBS; with a syringe and 32-gauge needle. After devices were filled, they were sealed using tape and placed in an incubator at 37° C. to simulate in vivo conditions. Fluorescent microscopy was performed using a Nikon Widefield fluorescent microscope (Nikon Instruments Inc., NY, USA). A series of fluorescent images of the channel region were acquired every 5 min for the first half hour and then every 2 hours for 12 hours, with a Hamamatsu camera (Hamamatsu, Shizuoka, Japan) using NIS Elements data acquisition software. Further images were taken at 12 h intervals for 2 days by stabilizing the device on a microscope stand for 30 min before acquiring the images. Image processing of time-lapse florescent images was performed using ImageJ (NIH, Bethesda, USA), to obtain the changes in florescent intensity across the channel at each time point. Briefly, pixel values were normalized by subtracting the background intensity value, and then divided by the maximum pixel value of 20 μM Dextran (concentration loaded in the reservoir). At each time point a plot of the normalized average intensity profile across the channel was generated. Thus, we could evaluate the generation of a spatially controlled concentration gradient by taking time lapse fluorescent images and measuring the changes in the fluorescent intensity across the channel to generate a diffusion profile.

The predictability of the mathematical diffusion model was evaluated by using a μFD and taking time lapse fluorescent images and measuring the changes in the fluorescent intensity across the channel to generate a diffusion profile. The fluorescence values were converted to the concentration values and compared with the values obtained using the mathematical diffusion model. The uFD was tested with the hole at distinct locations on the channel and compared with the mathematical model results. It was found that the mathematical model was predictive within ±10% of the measurement.

Example 7—Modeling of In Vitro Drug Release Over 30 Days

The purpose of this task was to evaluate and understand how the drug diffusion for compounds such as NGF or FK506 will be affected due to presence of biological tissue. It has been shown that drug diffusion in tissue could be characterized by reducing the aqueous diffusion coefficient of the molecule by half (D_(n)=D/2). The drug diffusion inside the device was simulated to understand how the drug concentration would vary inside the conduit lumen when tissue/nerve grew across the device and covered the hole. Drug release across the conduit was simulated over a period of 30 days with the device parameters of Reservoir volume: 10 ul, Reservoir concentration: 0.1 ug/ml. Table 1 lists the values for parameters that were used in the model.

TABLE 1 Parameters used with in vivo diffusion model Description Notation Value Unit Cross sectional area in the inner A₁₂ 7.85 × 10⁻⁷ m² conduit Cross sectional area in the proximal A₃₄ 6.36 × 10⁻⁷ m² nerve stump Wall thickness of the inner conduit L₁₂ 150 μm Diffusion coefficient in aqueous D 1.26 × 10⁻⁶ cm² s⁻¹ media Diffusion coefficient in nerve D_(n)  0.6 × 10⁻⁶ cm² s⁻¹ (D/D_(n) ~2)

Since the nerve growth will occur from the proximal to the distal end; the length l_(23prox) is variable. After 10-15 days of basal lamina repair, Schwann cell migration and endoneurial tube formation, the nerve growth rate varies broadly from 0.5 to 9 mm per day depending on the nature and severity of the nerve injury, the duration of denervation, the condition of the peripheral tissues and if the nerve gap length is less than critical gap for the animal model. For our mathematical model,

$\frac{\Delta\; l_{23{prox}}}{\Delta\; t} = {2\text{-}3\mspace{14mu}{mm}\text{/}{day}}$ was substituted after day 15. The presence of Schwann cells, endoneurial tubes and nerve growth was accounted for by reducing the diffusion coefficient. It has been shown that cellular membranes and the extracellular space (ECS), due to presence of fibrous tissue, would simply change the diffusion path length of the drug compared to diffusion in aqueous media, but would still allow the drug to go through. Based on these approximations, the drug concentration inside the device was evaluated. Based on the mathematical model, it was determined that the concentration released in the conduit lumen will be within the therapeutic range (0.1-10 ng/ml/day) over a period of 30 days. As the nerve repair progresses, infiltration of the device with basal lamina or Schwann cells will change the drug diffusion but at a rate that can be characterized by changing the diffusion coefficient in our model.

Example 8—In Vitro and In Vivo Drug Release Validation

In vitro and in vivo verification tests were performed to ensure that the nerve conduits released drug as expected. For the in vitro verification tests, the loaded devices were attached to the side wall of their respective receiver chambers where tests were conducted. A 5 mL transport tube was used as the receiver chamber for all of the tests conducted. PDMS was used to attach the devices to the wall in a location that would still allow for the devices to be fully submersed after the receiver chambers were filled with growth media. Samples were collected from the receiver chamber at predetermined time points. Sink method was used for drug collection. Once the fluid was collected, the receiver chamber was flushed and new medium was added to the chamber. After collection, samples were loaded into 96-well plates and amount of FK506 was determined using an enzyme-linked immunosorbent assay (ELISA) (FK506 Elisa; Abnova, Taiwan).

For the in vivo verification tests, the mice were anesthetized with isoflurane. The surgical area on the right hind limb was shaved and prepared with alcohol and betadine. A longitudinal (approximately 2 cm) incision was made in the posterior distal thigh of the hind limb, separating the natural muscle planes. Under the operative microscope, a 1.5 cm segment of the sciatic nerve was isolated. The sciatic nerve was transected to produce a 10 mm nerve gap. The device was sutured to the proximal and distal stumps of the sciatic nerve using a 9-0 nylon suture from the epineurium to the device maintaining the desired gap length.

In the in vitro test (n=4) it was found that the drug release matched the model outcome within a difference of ±10% (FIG. 10). Similarly, in the in vivo test (n=4) it was found that there was ˜15% drug left in the device at the end of 30 days (FIG. 10), which was within a reasonable error of that predicted by the model. Based on the model, 10% of the initially loaded FK506 should have remained within the device at the end of 30 days.

In vivo diffusion models have shown that the diffusion coefficient of a molecule in tissue is approximately half that of aqueous media [2, 10]. This preliminary data suggests that in vivo conditions (the presence of various hydrolytic/proteolytic enzymes; change in diffusion coefficient around tissue) has a slight effect on the release profile but it is within reasonable error of our predicted value.

To further validate that our device is releasing drugs in a predictive manner we implanted FK506 releasing devices for 1, 2, and 3 weeks and compared the amount of FK506 remaining in the reservoir with what was predicted by our model. The leftover drug in the device was used to estimate the amount of drug released at 1, 2 and 3 weeks and compared against model prediction. FIG. 11 shows the results for the in vivo FK506 release test as compared to the model prediction. The results show three favorable conclusions: first, the FK506 releases at a concentration that closely matches the diffusion model over the period of 30 days. Secondly, the FK506 was released at concentrations within the therapeutic range of 1-10 ng/mL. Daily in vivo release was slightly higher than the model predicted, with differences between the model and actual release diminishing with time. We also implanted FK506 loaded devices without a diffusion hole in vivo (n=3) and found that 95±2% of the FK506 (within margin of error of the ELISA) was remaining in the reservoir at 30 days. This confirmed that drug is not leaking or diffusing across the walls of the device.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope. 

The invention claimed is:
 1. A nerve repair conduit configured to be implanted in vivo, the nerve repair conduit comprising: a polymeric body having a proximal end, a distal end, an exterior surface and an interior surface, the interior surface defining an interior lumen of the polymeric body, wherein the polymeric body is configured to be secured to a first section of a nerve and a second section of a nerve to encourage repair of the nerve; a plurality of separate drug reservoirs positioned adjacent to the exterior surface of the polymeric body; an outlet arrangement formed at each of the drug reservoirs to provide fluid communication between the drug reservoir and the interior lumen of the polymeric body so as to enable delivery of an agent from the reservoir to the interior lumen of the polymeric body without requiring degradation of the polymeric body for release of the agent; and one or more dividers defining the separate reservoirs.
 2. The nerve repair conduit of claim 1, wherein the one or more dividers are oriented transverse to a longitudinal axis of the nerve repair conduit.
 3. The nerve repair conduit of claim 1, wherein the one or more dividers are oriented along a long axis of the nerve repair conduit.
 4. The nerve repair conduit of claim 3, wherein at least one of the plurality of separate drug reservoirs includes an outlet arrangement configured to provide an agent concentration gradient within the interior lumen of the polymeric body when the respective agent passes into the interior lumen.
 5. The nerve repair conduit of claim 4, further comprising an intermediate point between the proximal end and the distal end of the polymeric body, wherein the outlet arrangement configured to provide the agent concentration gradient includes a greater outlet surface area on a first side of the intermediate point relative to a second side of the intermediate point.
 6. The nerve repair conduit of claim 5, wherein the outlet arrangement configured to provide the agent concentration gradient includes a single hole positioned closer to the distal end of the polymeric body than to the proximal end of the polymeric body.
 7. The nerve repair conduit of claim 6, wherein the single hole is placed at a position located at about 55% to about 95% of the length of the interior lumen as measured from the proximal end of the polymeric body so as to provide the concentration gradient.
 8. The nerve repair conduit of claim 6, wherein the single hole is placed at a position located at about 60% to about 80% of the length of the interior lumen as measured from the proximal end of the polymeric body so as to provide the concentration gradient.
 9. The nerve repair conduit of claim 5, wherein the outlet arrangement configured to provide the agent concentration gradient includes multiple holes.
 10. The nerve repair conduit of claim 9, wherein a greater number of holes are disposed on the first side of the intermediate point than on the second side of the intermediate point.
 11. The nerve repair conduit of claim 10, wherein an average hole size is greater for holes disposed on the first side of the intermediate point than for holes disposed on the second side of the intermediate point.
 12. The nerve repair conduit of claim 9, wherein an average hole size is greater for holes disposed on the first side of the intermediate point than for holes disposed on the second side of the intermediate point.
 13. The nerve repair conduit of claim 4, wherein at least two of the separate drug reservoirs each include an outlet arrangement configured to provide respective agent concentration gradients within the interior lumen of the polymeric body when the respective agents pass from the separate reservoirs into the interior lumen.
 14. The nerve repair conduit of claim 1, wherein the one or more dividers are oriented orthogonal to a long axis of the nerve repair conduit.
 15. A nerve repair conduit configured to be implanted in vivo, the nerve repair conduit comprising: a polymeric body having a proximal end, a distal end, an exterior surface and an interior surface, the interior surface defining an interior lumen of the polymeric body, wherein the polymeric body is configured to be secured to a first section of a nerve and a second section of a nerve to encourage repair of the nerve; a drug reservoir positioned adjacent to the exterior surface of the polymeric body; an outlet arrangement formed at the drug reservoir to provide fluid communication between the drug reservoir and the interior lumen of the polymeric body so as to enable delivery of at least one agent from the reservoir to the interior lumen of the polymeric body without requiring degradation of the polymeric body for release of the agent, wherein the outlet arrangement is configured to provide an agent concentration gradient within the interior lumen of the polymeric body when the agent passes from the reservoir into the interior lumen; and an intermediate point between the proximal end and the distal end of the polymeric body, wherein the outlet arrangement includes a greater outlet surface area on a first side of the intermediate point relative to a second side of the intermediate point.
 16. The nerve repair conduit of claim 15, wherein the outlet arrangement includes a single hole positioned closer to the distal end of the polymeric body than to the proximal end of the polymeric body.
 17. The nerve repair conduit of claim 16, wherein the single hole is placed at a position located at about 55% to about 95% of the length of the interior lumen as measured from the proximal end of the polymeric body so as to provide the concentration gradient.
 18. The nerve repair conduit of claim 15, wherein the outlet arrangement configured to provide an-the agent concentration gradient includes multiple holes.
 19. The nerve repair conduit of claim 18, wherein a greater number of holes are disposed on the first side of the intermediate point than on the second side of the intermediate point; or an average hole size is greater for holes disposed on the first side of the intermediate point than for holes disposed on the second side of the intermediate point; or both a number of holes and an average hole size are greater on the first side of the intermediate point than on the second side of the intermediate point.
 20. A nerve repair conduit configured to be implanted in vivo, the nerve repair conduit comprising: a polymeric body having a proximal end, a distal end, an exterior surface and an interior surface, the interior surface defining an interior lumen of the polymeric body, wherein the polymeric body is configured to be secured to a first section of a nerve and a second section of a nerve to encourage repair of the nerve; a drug reservoir disposed concentrically around the exterior surface of the polymeric body, the drug reservoir including one or more dividers forming separate reservoir sections each containing a separate agent; an outlet arrangement formed at each separate section of the drug reservoir to provide fluid communication between the drug reservoir section and the interior lumen of the polymeric body so as to enable delivery of the separate agents from the reservoir to the interior lumen of the polymeric body without requiring degradation of the polymeric body for release of the agent, wherein each outlet arrangement is configured to provide a respective agent concentration gradient within the interior lumen of the polymeric body when the respective agent passes from the reservoir section into the interior lumen. 